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NE40E V800R010C10SPC500 Feature Description - Network Reliability 01

This is NE40E V800R010C10SPC500 Feature Description - Network Reliability
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Overview of VRRP

Overview of VRRP


The Virtual Router Redundancy Protocol (VRRP) is a fault-tolerant protocol that groups several routers into a virtual router. If the next hop of a host fails, VRRP switches traffic to another router, which ensures communication continuity and reliability.


In this document, if a VRRP function supports both IPv4 and IPv6, the implementation of this VRRP function is the same for IPv4 and IPv6 unless otherwise specified.

VRRP is a fault-tolerant protocol defined in relevant standards . VRRP allows logical devices to work separately from physical devices and implements route selection among multiple egress gateways.

On the network shown in Figure 5-1, VRRP is enabled on two routers. One is the master and the other is the backup. The two routers form a virtual router and this virtual router is assigned a virtual IP address and a virtual MAC address. Hosts monitor only the presence of the virtual router. The hosts communicate with devices on other network segments through the virtual router.

A virtual router consists of a master router and one or more backup routers. Only the master router forwards packets. If the master router fails, a backup router is elected as the master router and takes over.

Figure 5-1 Schematic diagram for a VRRP backup group

On a multicast or broadcast LAN (for example, an Ethernet), VRRP uses a logical VRRP gateway to ensure reliability for key links. VRRP prevents service interruptions if a physical VRRP gateway fails, providing high reliability. VRRP configuration is simple and takes effect without modification in configurations, such as routing protocol configurations.


As networks rapidly develop and applications become diversified, various value-added services, such as Internet Protocol television (IPTV) and video conferencing, have become widespread. Demands for network infrastructure reliability are increasing, especially in nonstop network transmission.

Generally, hosts use one default gateway to communicate with external networks. If the default gateway fails, communication between the hosts and external networks is interrupted. System reliability can be improved using dynamic routing protocols (such as RIP and OSPF) or ICMP Router Discovery Protocol (IRDP). However, this method requires complex configurations and each host must support dynamic routing protocols.

VRRP resolves this issue by enabling several routers to be grouped into a virtual router, also called a VRRP backup group. In normal circumstances, the master router in the VRRP backup group functions as a default gateway and provides access services for users. If the master router fails, VRRP elects a backup router from the VRRP backup group to provide access services for users.

Hosts on a local area network (LAN) are usually connected to an external network through a default gateway. When the hosts send packets destined for addresses out of the local network segment, these packets follow a default route to an egress gateway. A provider edge (PE) functions as an egress gateway on the network shown in Figure 5-2. The PE forwards packets to the external network so that the hosts can communicate with the external network.

Figure 5-2 Default gateway on a LAN

If the PE fails, the hosts connected to it cannot communicate with the external network. The communication failure persists even if another router is added to the LAN. This is because only a single default gateway can be configured for most hosts on a LAN and forward all data packets destined for devices that are not on the local network segment. Hosts send packets only through the default gateway though they are connected to multiple routers.

Configuring multiple egress gateways is a common method to prevent communication interruptions. This method is available only if one of routes to these egress gateways can be selected. Another method is to use dynamic routing protocols, such as the Routing Information Protocol (RIP), Open Shortest Path First (OSPF), and Internet Control Message Protocol (ICMP). This method is available only if every host runs a dynamic routing protocol and there is no problem in management, security, or operating systems' support for protocols.

VRRP prevents communication failures in a better way than the preceding two methods. VRRP is configured only on routers to implement gateway backup, without any networking changes or burden on hosts.


VRRP offers the following benefits to carriers:

  • Reliable transmission: A logical VRRP gateway on a multicast or broadcast local area network (LAN), such as an Ethernet network, ensures reliable transmission over key links. VRRP helps prevent service interruptions if a link to a physical VRRP gateway fails.

  • Flexible applications: A VRRP header is encapsulated into an IP packet. This implementation allows the association between VRRP and various upper-layer protocols.

  • Low network overheads: VRRP uses only VRRP Advertisement packets.

VRRP offers the following benefits to users:

  • Simplified configurations: Users only need to specify a gateway address without configuring routing protocols on their hosts.

  • Improved user experience: Users are not aware of a single point of failure.

Basic VRRP Functions

VRRP supports two modes: master/backup mode and load balancing mode.

Figure 5-3 shows the master/backup mode.

Figure 5-3 Master/Backup mode
For the master/backup mode:
  • A single VRRP backup group is configured and consists of a master device and several backup devices.
  • The router with the highest priority functions as the master device and transmits service packets.
  • Other routers function as backup devices and monitor the master router's status. If the master router fails, a backup router with the highest priority preempts the Master state.
Figure 5-4 shows the load balancing mode.
Figure 5-4 Load balancing mode
Multiple VRRP backup groups can be configured to implement load balancing. A single router can be a member of multiple backup groups. On the network shown in Figure 5-4, the VRRP backup groups work in load balancing mode.
  • PE1 is the master device in VRRP backup group 1 and the backup device in VRRP backup group 2.
  • PE2 is the master device in VRRP backup group 2 and the backup device in VRRP backup group 1.
  • In normal circumstances, different routers process different user groups' traffic to implement load balancing.
VRRP load balancing is classified as multi-gateway or single-gateway load balancing. For details about VRRP load balancing, see the chapter "VRRP" in HUAWEI NetEngine40E Universal Service Router Feature Description - Network Reliability.
Updated: 2019-01-03

Document ID: EDOC1100055045

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